This invention relates to a vacuum packaging apparatus for packaging articles or commodities such as beef, fish and the like by sandwiching them between two pieces of packaging material.
Vacuum packaging apparatuses of this kind are disclosed in U.S. Pat. No. 3,835,618, U.S. Pat. No. 3,129,545 and Australian Pat. No. 245,774. In each of these vacuum packaging apparatuses, the commodity is placed, in a vacuum chamber, on a piece of a lower packaging material such as thermoplastic film or reclaimed paper with plastic membrane on its surface and then is covered with a piece of an upper packaging material heated at a temperature approaching its melting point so that the upper packaging material can adhere to the lower packaging material with the commodity sandwiched therebetween.
The vacuum packaging apparatus of the U.S. Pat. No. 3,835,618 has a relatively large vacuum chamber in which large pieces of packaging material corresponding to the planar area of the chamber are used. Accordingly, this apparatus has an advantage in that a large number of articles of various shapes such as pieces of beef and fish can be easily packaged at one time in any desired disposition in the vacuum chamber. On the other hand, however, a relatively long period is required for obtaining again a desired degree of vacuum in the chamber when it is closed after the chamber has been once opened to take the articles after packaging out of the chamber. Thus, a time loss is incurred. The wasted period can be shortened by using a vacuum pump of large capacity. However, if such a vacuum pump were used, the pressure in the vacuum chamber of the apparatus would change excessively to cause the packaging material to be ruptured, and the heating time for the packaging material would be shortened to cause shortening of the heating time of the packaging material.
Furthermore, since the capacity of the pump to be used is limited for reasons of economy, a pump of a reasonable capacity should be selected, in which case, a period of at least about five seconds will be unavoidably required for obtaining a vacuum. In this case, there is a five-second wasted period during which the operator is idle, whereby an efficiency loss is incurred.
The vacuum packaging apparatus of Australian Pat. No. 245,774 also has only one vacuum chamber, and the operator must close and open the chamber manually to put the articles to be packaged into the chamber and take them out of the chamber. In this apparatus, also, the operator must wait without doing anything for the vacuum packaging to be completed.
In the apparatus of U.S. Pat. No. 3,129,545, as a plurality of vacuum chambers are mounted on a chain conveyor, such a wasted period is short. However, it not only needs a complex structure for driving the chain conveyor but also is bulky.
Accordingly, in a known attempt to solve this problem, a pair of vacuum packaging apparatuses are disposed in side-by-side arrangement, and the preparation for packaging is carried out in one of the apparatuses while the vacuum packaging is being carried out in the other. In this method, wasted idle period is eliminated, but it requires two apparatuses and is, therefore, uneconomical. More specifically, this method needs two vacuum pumps, either one of which does not operate during vacuum packaging operation, and two valve control systems for controlling valves in each apparatus.